The present invention relates to a medical examination apparatuses such as an X-ray CT apparatus.
When an operator takes an X-ray CT images of a patient using a conventional X-ray CT apparatus, he performs positioning of the patient according to the following steps.
(1) The patient places himself on a patient table. (In some cases, several operators move the patient from his bed to the patient table.)
(2) The operator places the patient into a scanner gantry by moving the patient table vertically and horizontally by manual operations. (Coarse patient positioning operation)
(3) A light source of a localizer (projector for the patient positioning) is turned on in response to the operator's operations on the patient table.
(4) Looking at a portion on the surface of the patient marked by light from the localizer, the operator determines (finely adjusts) an X-ray irradiating position.
(5) A scanogram image (X-ray CT image) is taken by X-ray irradiation.
(6) The scanogram image is displayed on an image monitor of an operation console. The operator determines, on the image monitor, an X-ray CT image taking position by using a track ball, for instance. At the same time, he determines X-ray CT image taking conditions and image reconstruction conditions. The image reconstruction conditions consist of a plurality of parameters such as the number of display matrices, a filter shape, a magnification factor and a reconstruction computing area.
(7) An X-ray CT image is taken, and an image analysis is performed thereon.
The conventional X-ray CT apparatus, in which the patient positioning is performed according to the above steps, has no interface between the light of the localizer and the image reconstruction conditions.
The localizer of the conventional X-ray CT apparatus will be described with reference to FIGS. 7 and 8.
As shown in FIG. 7, the X-ray CT apparatus has a top localizer 101, a left-side localizer 102 and a right-side localizer 103. Each of the localizers 101-103 is composed of a light source L, a slit S and a lens LE (and a mirror M).
It is a commonly employed scheme that the localizers 101-103 are linked with (i.e., turned on together with) a switch of the scanner gantry or patient table.
In the X-ray CT apparatus of FIG. 7, lines LN of light as a mark on the body surface of a patient PA is drawn as shown in FIG. 8 in accordance with, for instance, a cruciform aperture of the slit S. FIG. 8 shows a head HD of the patient PA, on which plural sets of cruciform lines LN of light are drawn.
Optics of each of the localizers 101-103 for generating the lines LN is fixed to the scanner gantry, and the width of tile cruciform aperture of the slit S is fixed. Therefore, it is impossible to change the with of the lines LN, nor move the lines LN of light themselves.
As shown in FIG. 9, in the conventional X-ray CT apparatus, the irradiation width (called "slice thickness" SW) of X-rays emitted from an X-ray tube 104 is varied with a part to be taken with X-rays. For example, the irradiation width is 10 mm when an abdomen is to be imaged; and is 5 or 2 mm for a head. Therefore, the lines LN of light of the conventional localizer basically serves to indicate only the center of the X-ray irradiation width.
With the above-described construction, the conventional X-ray CT apparatus has the following problems.
(1) It is hard for an operator to visually recognize the irradiation width (slice thickness SW) of X-rays emitted from the X-ray tube 104 from a marker (lines LN of light) of the localizer.
This problem results from the fact that the width of the lines LN of light cannot be changed because the optics of FIG. 7 are fixed to the scanner gantry and the cruciform aperture of the slit S is fixed.
(2) In the case of an X-ray CT apparatus capable of obtaining data in a "surface" (see FIG. 10) in contrast to the conventional X-ray apparatus of FIG. 9 in which an irradiation portion of X-rays emitted from the C-ray tube 104 has a "line" shape, the marker (lines LN of light) of the conventional localizer would be improper.
That is, the marker (lines LN of light) of the localizer cannot cover the X-ray irradiation width. This problem results from the facts that in the apparatus of FIG. 10 the values of the width W and the length D of a surface for data acquisition are much larger than the slice width SW of the conventional X-ray CT apparatus of FIG. 9, and that, as described above, the optics of the localizers 101-103 are fixed to the scanner gantry.
Referring to FIG. 11, a description will be made of a relationship between an X-ray irradiation area XR and an image reconstruction area FOV in the conventional X-ray CT apparatus of FIG. 7.
When an examination body (patient) PA is irradiated with X-rays emitted from the X-ray tube 104, data is obtained from all the irradiated area. However, an image processing device computes using image reconstruction area (FOV: field of view) that has been set in advance through an operation console, and an image corresponding to the image reconstruction area FOV is displayed on an image monitor 106.
The measurement data is stored in a storage device immediately after completion of the X-ray irradiation. Therefore, at a later time, the operator can reconstruct again an image corresponding to the image reconstruction area FOV and display it on the image monitor 106.
The image reconstruction area FOV is a circular area having, as its center, the center of the X-ray optical system (i.e., the center of the opening of the scanner gantry).
With the above-described construction, the conventional X-ray CT apparatus has the following problems.
(1) It is hard for an operator to visually recognize the reconstruction computing area FOV from a marker (lines LN of light) of the localizer.
This is so because, as described above, in the conventional X-ray CT apparatus the lines LN of light serve only as a marker for positioning an X-ray irradiating portion with no consideration made of the reconstruction computing area FOV. Further, the conventional apparatus does not have a function of causing a marker of the localizer to move in accordance with with the reconstruction computing area FOV. Such a function is not even necessary.
(2) The fact that the reconstruction computing area FOV cannot be recognized by use of the localizer leads to an increase of a time spent by a patient at examination and a reduction of the patient throughput.
Assume that X-ray irradiation is performed once and an X-ray CT image is obtained with a reconstruction computing area set by an operator from his experience. If a resulting displayed X-ray CT image lacks a portion to be monitored, image reconstruction may be performed again with data read from the storage device.
However, in some cases, this will cause an increase of a time spent by the patient at examination and a reduction of the patient throughput. That is, a time is required for the operator to judge whether a measurement has been performed correctly in an image reconstruction area FOV preset through the operation console. This problem can be avoided if the operator can correctly recognize in advance the reconstruction computing area FOV from a marker formed on the body surface of a patient PA.